DESCRIPTION: (Investigator's abstract): The studies will use cross-correlation analysis to examine neural interactions between the somatosensory thalamus and cortex during controlled cutaneous stimulation. The first experiment will test the hypothesis that thalamocortical cells elicit responses more effectively from middle cortical layers than from supra- or infragranular layers. Laminar differences in thalamocortical efficacy will have an important bearing on hypotheses regarding the sequence of information transmission between cortical layers. A related hypothesis concerns the strength of thalamocortical interactions in the horizontal cortical dimension. Studies will measure changes in this parameter as a function of somatotopic similarity/disparity between the thalamus and cortex. The last set of studies is designed to test the hypothesis that thalamic activity causes recipient cortical areas to inhibit neighboring cortical columns. Finally, in each of the experiments, special attention will be given to detecting the presence of corticothalamic interactions and determining whether these connections function to enhance or inhibit thalamic responsiveness.